1. Field of the Invention
The present invention relates to a pneumatic tire which can achieve an excellent hydroplaning performance and an irregular wear resistance while suppressing a groove wander.
2. Description of the Related Art
As one of factors affecting a rectilinear propagation stability of a vehicle, there is a wandering phenomenon of a vehicle called a groove wander. The groove wander has been known to be generated by a lateral force at a time when a side wall of a land portion of a tread falls in a rain groove, and a reaction force at a time when the falling portion comes into collision with a groove wall of the rain groove. The rain groove is a groove which is provided so as to be extended in a forward moving direction and has a fixed width for the purpose of securing a traveling stability at a time of raining, and is formed on Kyushu Jukan Expressway, freeway in California, U.S.A. and the like.
Conventionally, in order to prevent the groove wander, there is devised a countermeasure for making the side wall of the land portion hard to fall in the rain groove, by employing a pattern design in which the side wall of the land portion facing a main groove is inclined with respect to a tire circumferential direction. However, in the main groove with the pattern design mentioned above, since a see-through region is reduced and a draining efficiency tends to be lowered, in comparison with the main groove extending linearly in the tire circumferential direction, there has been a room for improving the hydroplaning performance. The see-through region means a region within the main groove which can be seen through without being obstructed the view by the right and left side walls, when viewed the main groove in the tire circumferential direction.
In a tire described in Japanese Unexamined Patent Publication No. 2002-2225, a groove wall close to a shoulder is inclined larger in a bent portion close to the shoulder than a groove wall close to a center, with respect to a main groove extending in a tire circumferential direction and having a zigzag shape, and a groove wall close to a center is inclined larger in a bent portion close to the center than a groove wall close to a shoulder. In this structure, since a see-through region is reduced due to the incline of the groove wall as mentioned above, a hydroplaning performance tends to be lowered. Further, even if the groove wall is inclined inversely, a rigidity of the bent portion is lowered and there is fear that an irregular wear is generated.